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>Chapter 38. Procedural Languages</H1
><P
>   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> allows user-defined functions
   to be written in other languages besides SQL and C.  These other
   languages are generically called <I
CLASS="FIRSTTERM"
>procedural
   languages</I
> (<ACRONYM
CLASS="ACRONYM"
>PL</ACRONYM
>s).  For a function
   written in a procedural language, the database server has
   no built-in knowledge about how to interpret the function's source
   text. Instead, the task is passed to a special handler that knows
   the details of the language.  The handler could either do all the
   work of parsing, syntax analysis, execution, etc. itself, or it
   could serve as <SPAN
CLASS="QUOTE"
>"glue"</SPAN
> between
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> and an existing implementation
   of a programming language.  The handler itself is a
   C language function compiled into a shared object and
   loaded on demand, just like any other C function.
  </P
><P
>   There are currently four procedural languages available in the
   standard <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> distribution:
   <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> (<A
HREF="plpgsql.html"
>Chapter 39</A
>),
   <SPAN
CLASS="APPLICATION"
>PL/Tcl</SPAN
> (<A
HREF="pltcl.html"
>Chapter 40</A
>),
   <SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
> (<A
HREF="plperl.html"
>Chapter 41</A
>), and
   <SPAN
CLASS="APPLICATION"
>PL/Python</SPAN
> (<A
HREF="plpython.html"
>Chapter 42</A
>).
   There are additional procedural languages available that are not
   included in the core distribution. <A
HREF="external-projects.html"
>Appendix G</A
>
   has information about finding them. In addition other languages can
   be defined by users; the basics of developing a new procedural
   language are covered in <A
HREF="plhandler.html"
>Chapter 49</A
>.
  </P
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